1. Field of the Invention
The invention relates to benzoic esters of 2-propylheptanol, of 2-propyl-4-methylhexanol, of 2-propyl-5-methylhexanol, of 2-isopropyl-4-methyl-hexanol and/or of 2-isopropyl-5-methylhexanol, to mixtures of these with alkyl phthalates, with alkyl adipates, or with alkyl cyclohexanedicarboxylates, and also to the use of these mixtures.
2. Discussion of the Related Art
Polyvinyl chloride (PVC) is one of the most important industrial polymers. It is used in a wide variety of applications, in the form of either unplasticized PVC or plasticized PVC.
To produce a plasticized PVC, plasticizers are added to the PVC, and phthalates are used in the majority of cases, in particular di-2-ethylhexyl phthalate (DEHP), diisononyl phthalate (DINP), or diisodecyl phthalate (DIDP). As the chain length of the esters increases, the solution or gelling temperatures rise, and therefore the processing temperatures of the plasticized PVC rise. The processing temperatures can be reduced again by adding what are known as fast-gellers, such as the short-chain phthalates dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), benzylbutyl phthalate (BBP), or diisoheptyl phthalate (DIHP). In addition to the short-chain phthalates, dibenzoates, such as dipropylene glycol dibenzoates or the like, may also be used for the same purposes.
A property frequently exhibited by these fast-gellers in PVC plastisols, owing to their high solvating power, consists in causing a marked rise in viscosity with time. In many cases this rise in viscosity must be compensated by adding viscosity-reducers.
When PVC plastisols are prepared, the general requirement is low viscosity and minimum gelling temperature. In addition to these, a high storage stability is desirable, i.e., a low rise in viscosity of the plastisol with time.
A high viscosity is burdensome on the machinery during processing of the plastisol. Excessively high gelling temperatures reduce the production rate.
Currently, there is little knowledge of plasticizers which significantly lower the gelling temperature in a formulation and also retain a low level of viscosity of the plastisol even after storage for a number of days. 2-Ethylhexyl benzoate was recently proposed as a product which could fulfill these requirements (Bohnert, Stanhope, J. Vinyl Addit, Technol. (2000), 6(3), 146–149). However, this compound has a comparatively high vapor pressure, which often leads to unacceptable losses during processing.
DE 19 62 500 discloses the use of a mixture of relatively long-chain esters of benzoic and phthalic acid for preparing plastisols. 3,5,5-Trimethylhexanol is preferably used to prepare the benzoic esters. No precise information is given concerning the phthalic diesters to be used. U.S. Pat. No. 5,236,987 discloses the use of benzoic esters of isodecanols which have exclusively methyl branching as plasticizers or gelling agents for PVC.
The use of alkyl benzoates whose alkyl group has from 11 to 14 carbon atoms is disclosed in WO 97/39060. Although relatively long-chain esters have low volatility, they have poorer gelling properties.
In PVC, the abovementioned plasticizer systems are not completely satisfactory, and there is room for improvement not only in their volatility but also in their gelling properties, in low-temperature flexibility, and in storage stability. When preparing plasticized PVC, gelling capability has to be good and the volatility of the plasticizer has to be low. This is affected by the interactions between plasticizer and PVC polymer chain, and even slight structural changes in the molecular structure of the plasticizer molecule can therefore bring about large changes in performance characteristics.